In the context of next generation wireless network, with a targeted commercialisation time around year 2020-2025, millimetre wave radio is considered to be used for the purpose of e.g. establishing a backhaul link for an access point/network node, as well as the access link between the access point/network node and a mobile terminal. The backhaul nodes may be e.g. aggregation and non-aggregation backhaul nodes. The non-aggregation backhaul node is usually associated with an access node (or access point, or base station, or Node B or eNode B/eNB). The backhaul nodes can be installed e.g. on building walls or lamp posts while the aggregation nodes can be installed on a building top. The aggregation backhaul node is used to aggregate signals from multiple non-aggregation backhaul nodes. The aggregated backhaul signals are then transported further to other network nodes for processing.
Millimetre wave is the radio wave with wavelength between 1 mm and 10 mm, corresponding to frequencies from 30 GHz to 300 GHz. Due to the large chunk of available spectrum bands, millimetre wave is preferable for carrying high bit rate data on the backhaul link. However, it may be noted that spectrum bands other than bands between 30 GHz and 300 GHz can also be used for the backhaul link. Equipment and methods can be used for those bands in the same principle as disclosed.
Backhaul link is one of favourable use cases for millimetre wave communications as the nodes are usually fixed and there are Line of Sight (LoS) links between nodes. Nevertheless, millimetre wave communications can be used for access links as well.
Backhaul link between the backhaul node and the aggregation node shall provide very high data transmission capability to support high data services for future generation mobile devices. For example, in case of so-called “front hauling” scenario where the radio frequency signals to/from mobile devices are directly sampled and sent from/to central processing units, the data transmission requirement is much higher than a usual “back hauling” scenario where only baseband signals are sampled.
One way to boost channel capacity of millimetre wave based backhaul link is to use Multiple-Input-Multiple-Output (MIMO) configuration (and very often LoS MIMO) for transmitter and receiver of the backhaul link. One typical LoS MIMO system is using Uniform Linear Arrays (ULAs) for transmitter and receiver.
In such a system, the transmitter and the receiver antenna arrays comprise multiple antenna sub-arrays. The subarrays are using multiple antenna elements to form narrow beams. The inter-subarrays distance is Dt and Dr respectively for transmitter and receiver. The parameters θt and θr are the down tilting angles for transmit antenna and for receive antenna respectively, as illustrated in FIG. 1, depicting a transmitter and receiver antenna arrays.
A narrower beam width is achieved with a higher number of antenna elements in the array. Advantages therewith comprise increased interference protection and spectrum reuse via boosted beamforming gains. The highly directional and narrow radiation pattern from high-order millimetre wave MIMO radios allows many radio devices to be deployed near each other without causing troublesome interference even when they are using the same frequencies.
Narrower beam is beneficial for the purpose of providing higher antenna gains, causing less multi-path fading as well as minimising cross link interference. To establish and maintain a link between transmitter and receiver via narrow beam requires however consideration for the design, operation and optimisation of the millimetre wave radio system.
To adjust antenna elements of the transmitter by motorised electromechanical adjustments is known. However, these adjustments take time.
However, the direction of the antenna beam may change in a possibly fast and unpredictable manner, in particular when the transmitter and/or the receiver is mobile. The transmitter and the receiver may be moved around, in relation to each other, linearly and also turned around angularly around different axis. In order to establish and uphold the radio connection between transmitter and receiver, it is important to direct antenna beam of the transmitter/receiver towards each other quickly, when the relative movements between transmitter and receiver is fast.
In case the connection link between transmitter and receiver is lost, there is no convenient way of recovering the lost connection link, besides restarting the whole access process.
Also, nodes which traditionally are not regarded as “mobile” such as a backhaul node and/or access node situated e.g. in lamp posts, poles, masts or similar, may be moving in relation to each other due to e.g. windy conditions, earth quake, land slide or similar phenomenon, which in some cases may cause a lost communication link if transmitter/receiver antenna elements are not adjusted fast enough.
It would thus be desired to encounter a faster way of adjusting antenna elements of a transmitter/receiver in order for millimetre radio to become feasible.